The present invention relates generally to locating buried cables, and more particularly to locating buried non-conductive cables.
Recent years have seen a proliferation of telecommunication services. With the additional services has come an increased need for network infrastructure, including in particular, buried cables and associated equipment. Along with this proliferation comes the need to determine the location of buried cables. The location of buried cables is necessary for various purposes, for example to avoid damage during excavation operations, or to repair previously damaged cable.
One known technique for locating buried cable is the application of an electrical signal to a metallic portion of the cable, and using a receiver (usually at the surface) to detect the magnetic fields generated by the applied signal. The applied signal is generally an alternating current (AC) signal. The resultant location signal which is radiated along the length of the cable is detectable by detection equipment. The ability to detect the cable at various distances and depths is dependent upon the type of applied signal, the type of the cable and the ground conditions. Such a technique is well known in the art.
However, a problem presents itself in that telecommunications companies have thousands of miles of non-conductive fiber cable contained in buried duct structures beneath metropolitan streets. This fiber cable is known as “dielectric fiber”, meaning it contains no metallic strength members. While dielectric fiber has the advantage of lower cost, it also has the disadvantage that it cannot be located electronically. Since dielectric fiber is non-conductive, the above cable locating techniques cannot be used. While maps may be made during installation of these cables, such maps are often inaccurate and/or outdated.
What is needed is a practical system and method for mapping non-metallic fiber ducts to allow for cable location.